DOHUK, Kurdistan Region -- A Kurdish official dealing with Yezidi refugees said there was "solid evidence" of mass executions by the Islamic State armies, as a UN mission heads to Iraq to investigate rights violations by the militants.

Dr. Nuri Usman, who is in charge of a special office set up the Kurdistan Regional Government (KRG) for the return of Yezidis made homeless by an IS attack on their villages last month, declined to speculate about the numbers of dead.

"There have clearly been mass executions. It may take years to even understand how and how many have been killed or abducted," he said.

"We have solid evidence that nearly 100 Muslim Kurds were executed. The Islamic State does not differentiate between Muslim Kurds or Yezidi Kurds."

He also said the KRG is trying to rightfully influence the international community to recognize the mass killings in Shingal as an act of genocide and has gathered sufficient evidence for it.

"We have collected a great number of images and videos that confirm the massacre as a clear act of genocide."

Last week, the United Nations said it was sending a mission to Iraq to investigate rights violations by the Islamists, but also by the Iraqi government and groups associated with it.

Usman was confident the refugees from Shingal would return to their homes, saying recapture of the town from the militants is "just a matter of time." The Kurdistan Workers Party (PKK) and the People's Protection Unit (YPG), whose forces are reportedly present on the grouns, stated last month that the efforts to recapture Shingal should be coordinated with their military forces.

More than 600 school buildings were allocated to accommodate the refugees in Dohuk province, Usman said. He said schools are likely to start later than usual this year "but the KRG will do its utmost to relocate the refugees into proper camps."

Usman said the work of his office will go on as long as the Shingal refugee crisis continues.

"We're in constant contact with many international organizations and NGOs and try to help them understand the instant needs of these refugees," he said.

He added that a reliable assessment of the number of the refugees was impossible at the moment. "The refugees are not staying only in one place. Some are in Erbil, some stay with their relatives. Nearly 7,000 refugees are still on the Shingal Mountain. So it's difficult to know the exact number."

According to Usman, more than 5,000 people decided to stay in Shingal and the surrounding villages.

"We have supplied them with food and water. They want to stay there (the Shingal area), because some of them have livestock and don't want to abandon their livelihood."